This invention relates to a method of marking and evaluating screen displays or for taking measurements therein, particularly in connection with section displays generated by the ultrasonic pulse-echo method, wherein a light pen is used, which in an operative position directs a receiving optical system against fluorescent screen areas that are brightened by the electron ray and by an amplification or transformation of the light received by the optical system from said areas generates bright-up pulses for intensifying the electron beam as it scans the area to which the light pen is directed so that a light spot appears in said area.
The invention relates also to equipment for carrying out said method, comprising a fluorescent screen unit having a fluorescent screen on which an electron beam is adjustable, particularly line by line, by deflecting means, whereas the intensity of said electron beam is controlled by brightness control means, and a light pen which generates bright-up pulses for the electron beam under control of a receiving optical system that is responsive to the brightness of the fluorescent screen.
It is often necessary to take measurements in screen displays or to ascertain the relation of a plurality of different targets. It is also often desired to emphasize specific regions of a display by additional marks. Such problems arise also in section displays generated on a screen as a result of ultrasonic examinations. The problems involved will now be discussed mainly in connection with such section displays. In the simplest case it is necessary to measure the coordinates of a given point of the display. It may also be necessary to ascertain the distances between two or more different points or in complicated cases the length even of irregularly curved lines or to determine the area of regions which may be defined at least in part by irregular lines. A direct measurement on the fluorescent screen would be inaccurate because optical distortions and a resulting parallax error must be expected owing to the thickness of the fluorescent screen and of a protective pane which may be disposed in front of the fluorescent screen. Additional distortions may arise mainly in marginal regions of a fluorescent screen as a result of structure-induced influences on the movement of the electron beam and which also adversely affect the accuracy of measurements taken directly on the fluorescent screen by directly applied measuring instruments. In an endeavour to eliminate these errors at least in part, it is known to take a photograph of the screen display and to take the required measurements on the photograph, although that practice will not eliminate the errors due to marginal distortion and does not save a substantial amount of time regarding the taking of the measurement. On the contrary, there is a lapse of time until the photograph has been developed so that the evaluation cannot be effected virtually simultaneously with the observation of the fluorescent screen, as is often desired. Whereas it is known to include scales or adjustable light marks in the screen display, that practice permits only a measurement of the distance between individual points and involves a comparatively high electronic expenditure. It is desirable for an increase of the accuracy of the measurement and of the speed with which measurements can be taken to provide simple means by which data that can be obtained from the fluorescent screen can be delivered as direct as possible, without intermediate processing, and without parallax errors, to computers by which the desired evaluation is effected in accordance with preselectable programs.
In television engineering it is known to provide a so-called light pen, with which certain points on a fluorescent screen can be marked. Such a light pen comprises an optical system, which forms an image of a small portion of the fluorescent screen on a photoelectric transducer inside the light pen when that light pen is applied to the fluorescent screen. As the surface element represented by the image is brightened by the electron beam, the light pen generates a bright-up pulse which is delivered by an amplifier to the means which control the intensity of the electron beam so that a light spot is generated near or in the region to which the light pen is applied. That light spot is always generated to have a width corresponding to a plurality of lines. In the previous practice such light spot has only been used to direct the attention to selected portions of the fluorescent screen being observed but the use of the light pen for a determination of coordinates has not yet been contemplated. At best, the light pen could be directed to the interesting points in succession and the measuring instrument could then be directed to the same points. Because the light spot is always relatively large, an exact adjustment is not possible. In the known use of the light pen, its optical system delivers light pulses which represent the average brightness of that portion of the fluorescent screen which is being sensed. This results in the basic disadvantage that the light pen fails in the known arrangement unless part of that region of the fluorescent screen to which the optical system of the light pen is directed has areas which are sufficiently bright so that the optical system can induce a response of the photoelectric transducer because otherwise a bright-up pulse cannot be generated. It is apparent that the conventional light pen cannot be used to mark dark picture areas. In an effort to eliminate this disadvantage, a highly expensive arrangement has been proposed which comprises two fluorescent screens, in which the vertical and horizontal sweep, respectively, are synchronized. Only one fluorescent screen displays the desired picture because its electron beam is modulated in accordance with the instantaneous brightness of the picture. The second fluorescent screen exhibits a display of constant brightness. The light pen is applied to the latter fluorescent screen and the pulses generated by the light pen are amplified and used to brighten the first fluorescent screen at a point which corresponds to the point at which the light pen is applied to the first fluorescent screen. As a result, even entirely dark areas of the image can be marked. In that arrangement, too, the light spot which is generated is relatively coarse and can hardly be used for exact measurements. The area of the fluorescent screen to which the optical system of the light pen is applied has a diameter corresponding to some line widths and the light spot has a correspondingly large diameter.